iio: temperature: mlx90632: Interface to change object ambient temperature

Since object temperature might be different than the sensor temperature
the infrared sensors should provide an interface to inject ambient
temperature. This was in past done via write to ambient temperature
interface (in_temp_ambient_raw), but I think most people did not know
about it. This solution introduces a new iio type of the CALIBAMBIENT
which is hopefully more descriptive and more explicit about the purpose
and capabilities of the sensors.
Signed-off-by: Crt Mori <cmo@melexis.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20200906210231.383976-1-cmo@melexis.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio

@@ -1758,6 +1758,14 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		One of the following thermocouple types: B, E, J, K, N, R, S, T.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_temp_object_calibambient
+What:		/sys/bus/iio/devices/iio:deviceX/in_tempX_object_calibambient
+KernelVersion:	5.10
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Calibrated ambient temperature for object temperature
+		calculation in milli degrees Celsius.
+
 What:		/sys/bus/iio/devices/iio:deviceX/in_intensity_x_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_intensity_y_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_intensity_z_raw

drivers/iio/industrialio-core.c

@@ -166,6 +166,7 @@ static const char * const iio_chan_info_postfix[] = {
 	[IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity",
 	[IIO_CHAN_INFO_OVERSAMPLING_RATIO] = "oversampling_ratio",
 	[IIO_CHAN_INFO_THERMOCOUPLE_TYPE] = "thermocouple_type",
+	[IIO_CHAN_INFO_CALIBAMBIENT] = "calibambient",
 };
 
 #if defined(CONFIG_DEBUG_FS)

drivers/iio/temperature/mlx90632.c

@@ -761,7 +761,9 @@ static int mlx90632_read_raw(struct iio_dev *indio_dev,
 			*val2 = data->emissivity * 1000;
 		}
 		return IIO_VAL_INT_PLUS_MICRO;
-
+	case IIO_CHAN_INFO_CALIBAMBIENT:
+		*val = data->object_ambient_temperature;
+		return IIO_VAL_INT;
 	default:
 		return -EINVAL;
 	}
@@ -781,6 +783,9 @@ static int mlx90632_write_raw(struct iio_dev *indio_dev,
 			return -EINVAL;
 		data->emissivity = val * 1000 + val2 / 1000;
 		return 0;
+	case IIO_CHAN_INFO_CALIBAMBIENT:
+		data->object_ambient_temperature = val;
+		return 0;
 	default:
 		return -EINVAL;
 	}
@@ -798,7 +803,7 @@ static const struct iio_chan_spec mlx90632_channels[] = {
 		.modified = 1,
 		.channel2 = IIO_MOD_TEMP_OBJECT,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
-			BIT(IIO_CHAN_INFO_CALIBEMISSIVITY),
+			BIT(IIO_CHAN_INFO_CALIBEMISSIVITY) | BIT(IIO_CHAN_INFO_CALIBAMBIENT),
 	},
 };
 

include/linux/iio/types.h

@@ -59,6 +59,7 @@ enum iio_chan_info_enum {
 	IIO_CHAN_INFO_CALIBEMISSIVITY,
 	IIO_CHAN_INFO_OVERSAMPLING_RATIO,
 	IIO_CHAN_INFO_THERMOCOUPLE_TYPE,
+	IIO_CHAN_INFO_CALIBAMBIENT,
 };
 
 #endif /* _IIO_TYPES_H_ */